In a previous post (My Garden In Summer – E. A. Bowles, 1865-1954 – Roses) we touched upon the subject of aestivation and Bowles discussed the ancient riddle of the “five brothers”; he described its understanding as being for those “fond of mental arithmetic”. At the time, I noted that I had read another account of the brothers, somewhere in my library, and that I would post it if it could be found. It has been found in The Rose’s Kiss, A Natural History of Flowers by Peter Bernhardt and I post it here.
Bernhardt’s book is very informative and his clear and imaginative writing goes a long way to relieving the mental arithmetic, not only of the five brothers but of the confusing nomenclature and myriad details of botany, that can make understanding of horticultural knowledge difficult for amateurs like myself. It explains the origins of the scientific names for plants, and for plant parts and processes as well as their interactions with creatures in our natural world that depend on them and which, by pollinating plants and disbursing their reproductive agents, ensure their (and thus our) continued survival.
I would recommend this book to anyone in need of a refresher course in botany that will not bore – but that will, rather, entertain as it informs. Our excerpt, Chapter 1, is an excellent explanation of plant classification and reproduction. The book is available for sale at the above link as well as another excerpt, When to Bloom, available here.
Above: The “five brother’ sepals that make up the calyx of a dog rose (Rosa canina). Below: Floral rings and organs in a garden rose. Illustrations by J. Myers.
The Rose’s Kiss
A Natural History of Flowers
Shearwater/Island Press, 1999
Hardcover, 267 pp
Brotherhoods and Sister’s Rooms
On a summer’s day, in sultry weather, Five brethren were born together.
Two had beards and two had none, And the other had but half a one.
“The Five Brethren,” trans. Edward A. Bowles
Many versions of this riddle are found in Latin, English, and German. It’s older than Europe’s first printing press. It may have been written by Albertus Magnus (ca. 1200-1280), a Dominican friar and plant hunter who became bishop of Regensburg and an early authority on soil fertility. It’s hard to associate this brainteaser with such a serious man. After all, this is the same Albertus Magnus who convinced the Poles to stop killing their crippled children.
Can you guess the answer to the bishop’s riddle? It would help if you could go out into the garden and pick a dog rose (Rosa canina). If you don’t have a dog rose, any of the fancy breeds based on hybrids with dog rose “parents,” such as Abbotswood, Cheshire, Blanche Superbe, Maiden’s Blush, or the White Rose of York, will do. You won’t need a microscope, but one of those big, cheap plastic magnifying lenses sold in most coin and stamp shops will give you the fine detail you’ll need in order to see the five brothers.
First, turn your rose upside-down and find the narrow, flat, green triangular organs that make up the lowest and outermost ring on your flower. Each of these triangles is known as a sepal. The word sepal comes from the Latin word for “separate.” Your rose should have five sepals. In a fully open flower, each sepal has a separate, pointed tip.
Now examine the margins of each sepal. Two sepals will have edges that break up into tiny, flattened “whiskers.” They are the bearded brothers. Two will have smooth edges, so they can be counted as the beardless brothers. The brother with only half a beard has one smooth edge and one whiskery edge.
Sepals are usually the most leaflike parts of a flower, regardless of species. They tend to contain the same number and arrangement of veins found in the foliage, the true leaves growing on the branches below the flowers. Sepals are often as green as true leaves because they, too, store the pigment chlorophyll. This is the same chlorophyll that makes it possible for true leaves to capture energy from sunlight and then store it in sugar molecules. The skin cells of both sepals and leaves are transparent. That’s why we can see the green chlorophyll, which is packed into a horizontal layer of cells arranged directly underneath the colorless skin.
Like leaves, most sepals have functional breathing pores on their skins. These breathing pores are flanked by guard cells that shut the pores when conditions become too arid. On dry days, closed pores help keep leaves from losing too much moisture in the form of vapor. Sepals may help keep other parts of the flower moist while they grow inside the bud.
Together, the five sepals form a ring called the calyx. Calyx is derived from a Greek word referring to a husk or envelope. The calyx is so named because it usually forms the bud of a young flower, sheathing and protecting the internal organs. The calyx does not divide into sepals until all the inner organs of the flower are ready to emerge and unfold.
The buds of some flowers wear an outer coat of sharp prickles or gluey glands. These ornaments may offer even greater protection to the young flower by discouraging insect attacks. In a few flowers, sepals are discarded as the flower opens. The sepals of poppies (Papaver), bleeding hearts (Dicentra), and fumitories (Fumaria) are little more than thin wrappers that fall to the ground once the inner organs are mature and the sepals’ job is done.
In later chapters, you will see how the sepals of some other flowers do far more than act as mere protectors. These sepals may be retained for the full life of the flower and even become a part of the ripened fruit.
As important as sepals are, no one loves a rose for its calyx. Poets and artists would rather praise the petals, which are anchored above the calyx. The word petal comes from the Late Latin petalum, meaning “metal plate or blade.” Together, a ring of petals makes a corolla. In Latin, corolla (diminutive of corona) means “little crown.” This makes sense, since crowns are often made of a simple hoop of united metal plates or points.
The anatomy of a rose petal gives it its light, silky, and gaudy quality, which is so absent in sepals. The petals of most flowers usually contain only one or three veins. Petals house their bright pigments in cells that make up the outer layers of skin. The interior of a petal contains spongy tissue, but the individual cells are packed so loosely that lots of air pockets form. Although the petals of many flowers bear pores and unusual sculpting, these structures serve a different purpose from that of the sepals, as you will see in later chapters. It appears that such features are more likely to attract, reward, and recruit visiting animals.
To be honest, though, the difference between petals and sepals is often obscure. In some species, no obvious difference between petals and sepals can be seen, either with the naked eye or with the help of a microscope. Such flowers contain one to several rings of flat structures that have the same color and shape and the same number of veins. Sometimes these organs aren’t even arranged in discrete rings. Instead, they are arrayed in a continuous spiral, like steps in a grand staircase.
When botanists can’t find either an internal or an external difference between sepals and petals, they call the organs tepals. Plants as different as star anises (Illicium), magnolias (Magnolia), rushes (Juncus), water hyacinths (Eichhornia crassipes), and irises (Iris) have flowers with tepals arranged in rings or spirals.
The corolla of a wild rose usually contains just five petals in one distinct ring. However, your garden flower may tell a completely different story. Sometimes a single bloom will contain dozens of petals crammed into a dense, confusing package. Outside the garden, these “sports,” or mutations, are usually eliminated by natural forces, since the flowers are not always hardy. It’s possible that having too many petals also wastes limited construction materials, lowering seed set.
However, shrubs with mutated blossoms have been carefully protected and propagated by the human hand, giving us gardens filled with “double” flowers and hundred-petal roses. These plants have been prized for thousands of years. The Greek philosopher Theophrastus (ca. 372 – ca. 287 B.C.), a pupil of Plato and Aristotle, commented on the protection and cultivation of such pretty errors in heredity. He wrote that most were grown near Philippi and were purchased from people who dug up mutant shrubs on Mount Pangaeus. Although extra petals represent developmental errors in rosebuds, in the next chapter you will see how they can help us understand the course of floral evolution.
Sepals and petals are always sterile organs in a flower, since both structures lack the cells needed to make either pollen grains or seeds. That all changes, though, when you leave the corolla and find the rings of stamens in your rose. Stamen is Latin for “warp thread” because stamens often resemble loose threads or pieces of yarn. Furthermore, stamens tend to be arranged lengthwise in a flower, like the warp threads on a loom.
Primitive and advanced sex organs. Above left: The flat, leaflike stamen of a Degeneria. Above right: “Lollipop” stamen of a rose. Below right: Bottle-shaped carpel of a rose. Below left: Rounded carpel of a Degeneria. Illustrations by J. Myers.
There are some unusual exceptions to this rule. You won’t find “stringy” stamens in the large flowers of some trees and shrubs, such as magnolias, star anises, Carolina allspice (Calycanthus floridus), and custard apples (Annona). Nor will you find them on the blossoms of some tender water plants, such as hornworts (Ceratophyllum), arrowheads (Sagittaria), and many members of the waterlily family (Nymphaeaceae). All these flowers have stamens that are peglike or paddle shaped. Chunky or flat stamens should contain three major veins, and there should be two or four sacs embedded in the flesh of each peg or paddle. Pollen is made inside each of these sacs.
Fossil evidence suggests that the stubby peg or paddle shape represents the oldest form of stamen. Over a period of 110 million years, plants that made flowers with skinny, stringy stamens topped with “lollipop” heads began to replace plants that made blossoms offering only chunky or flat stamens. The lollipop design triumphed, and it now dominates most of the flowering species on this planet, including the dog rose. Each stringy stamen is subdivided into two interconnecting parts, the filament and the anther.
The filament is just the long, cylindrical stalk that makes up most of the narrow length of the stamen (the word filament comes from the Latin word filum, “thread”). The filament is usually so narrow that it contains only one long vein. Close inspection of the swollen “lollipop” head of a stamen reveals that it is really made of paired sacs. This knobby head is called the anther.
Although the names of most of a flower’s organs relate to their special shapes, the word anther derives from an odd bit of medical Latin. Anther once referred to a special kind of medicine made by extracting the juices and oils of flowers. Earlier generations of botanists seem to have had a good reason for calling the knobby tip of a stamen the anther. The sacs of each anther contain a most important “extract” essential to plant reproduction.
The anthers of most flowers release pollen as fine, dry grains. The Latin word pollen means “a fine powder or flour.” Consequently, the botanical term pollen shares the same linguistic root as polvo, the Spanish word for dust, and polenta, the Italian word for a savory dish made of cornmeal.
By the late seventeenth century, some naturalists were comparing the pollen grains in an anther sac to sperm in an animal testicle. Stamens were seen as the “male majority” inside a flower. That’s why the ring of stamens in a flower was named the androecium, a Greek word that alludes to domestic arrangements commonly attributed to homes in ancient Athens. In the days of Socrates and Aristophanes, men were entitled to occupy apartments in their houses separate from their wives and daughters.
In most flowers, the androecium is composed of one or more rings in which individual stamens are arranged in an orderly single file. Exceptions to this rule are interesting to examine with a hand lens. For example, the stamens of most St. John’s worts (Hypericum), peonies (Paeonia), and some guinea flowers (Hibbertia) form discrete clumps or bundles, with each clump made up of two to eleven stamens. Sometimes all the stamens in these bundles interconnect at their base and share a common trunk and vein, so the stamen cluster resembles a hand of pointing fingers or a miniature candelabra.
A wild rose often contains several rings of male “apartments.” Has any room been left in the blossom to accommodate females? The answer is yes. The same naturalists who saw stamens as male organs believed that the separate structures containing young seeds were womblike and unquestionably feminine. The gynoecium (from the Greek gynaeceum, meaning “women’s apartments”) lies in the center of the rose, encircled by the rings of stamens. Since the little organs that make up the gynoecium form both the final and the central part of the flower, they are organized in a clumped, continuous mass.
The gynoecium of the rose is made of greenish yellow, bottle shaped organs known as carpels. Carpel is derived from the Latin carpellum and the Greek karpos, both of which mean “fruit.” Cut open the base of the rounded bottom of any flower’s carpel and you should find one to thousands of round or egg-shaped bodies inside. These structures, called ovules (from the Latin ovulum, diminutive of ovum, “egg”), are immature seeds waiting for sperm. That’s why the swollen base of each carpel is properly called an ovary and why botanists named the centralized mass of carpels after a dormitory for women. Fertilize a carpel’s ovules with sperm from pollen grains and it will almost certainly mature into a seed-filled fruit.
Every flower, then, is really a tightly compressed branch specialized for producing seeds. Within every flower, rings or spirals made of differently modified leaves play different roles in seed production. Botanists currently recognize five different living divisions of seed-making plants. However, members of only one division, the Anthophyta, make seeds inside real flowers. What distinguishes a rose flower from “nonflowers” such as the rigid pine cone (Pinus), the squashy, fragrant cone of a juniper bush (Juniperus), the red seed cup (aril) of a yew (Taxus), or even the spur-shoot of lumpy seeds dangling from the twig of a maidenhair tree (Ginkgo biloba)?
Pines, junipers, yews, and ginkgos are some of the seed plants that always allow their ovules to grow on a thin scale exposed directly to the air. These trees and shrubs are called gymnosperms, from the Greek words gymnos, “naked,” and sperma, “seed.” The ovules hang naked in the breeze, waiting for pollen grains provided by puffy male cones. A gymnosperm ovule always has a single, wet pore on its outer surface to catch pollen blown by the wind or carried by a beetle or moth. Some gymnosperms give their ovules extra protection in the form of hard, flattened leaves that form tough “shingles” and attach themselves to each scale and its ovules. These shingles arrange themselves in a continuous spiral, forming the familiar female cones of pines, firs, cedars, cycads (a distinctive division of palmlike gymnosperms that survived the Age of Dinosaurs), and their kin.
If you could look into even the youngest flower bud of a rosebush, you would see a burst of development that makes all true flowers unique. The carpel starts to grow as would any flat leaf or the thin, flat scale of a gymnosperm. Eventually, one to many ovules may form as bumps on the upper surface of this carpel “leaf.” However, before the ovules can mature, the carpel closes up, locking the ovules inside a chamber. A carpel may simply fold over on itself, enclosing the ovules as if they were pearls inside the two valves of an oyster’s shell. Or the process may occur more smoothly, with the carpel curving along its own margins until the edges meet to form a cylinder, a living bottle in which to store the ovules.
The closed carpel is the only thing that makes a flower a flower. That is why all flowering plants are called angiosperms, from the Greek words for seeds (sperma) inside a vessel (angeion). The sperm inside a pollen grain can reach the ovule only by moving along a prescribed, specialized route, but that route is found in every carpel.
To maintain its unique shape and function, a carpel usually contains more veins than does any other organ in the flower. Ovaries have a base number of three veins, but five are common, and even more are found in some species. Each ovary has one or two structures attached on top. As is the case in most flowers, each rose carpel has a stalky or pin-shaped “neck” called the style. Indeed, the word style is from stilus, a Latin word for the ancient pin-shaped tool used to engrave words onto wax tablets. In turn, each style is tipped by a glandular head called the stigma. Stigmas are usually swollen and may be ornamented with weeping scabs, pimples, or fleshy warts. It is no surprise that in Latin, stigma refers to a stab wound or a scar left by a branding iron.
To reach an ovule inside the ovary of a true flower, a pollen grain must first adhere to a stigma. The sperm must then leave the interior of the pollen grain and travel down the style to the ovary. I will save the travelogue of the adventurous sperm for a later chapter.
Meanwhile, it can be said that although each true carpel has a stigma, some carpels lack styles. The carpels in flowers of magnolias, star anises, custard apples, Australian spice bushes (Eupomatia laurina) , and Winter’s bark trees (Drimys) never grow styles. In these flowers, the stigma is a slit, cap, or crest directly ornamenting the surface of the ovary. According to the fossil record, the absence of a style seems to be a relic of older, “unsophisticated” times in flower evolution. Not surprisingly, carpels lacking styles are often found within the same flowers that have retained peglike or paddle-shaped stamens. Some scientists have compared fossils with living plants and concluded that short, squat floral organs evolved before most pollinating insects developed either longer mouthparts or forelegs that could push, clutch, or otherwise manipulate floral organs. The descendants of some of these less specialized insects survive to this day. In later chapters, you will see how they feed within the interiors of these same flowers, rather like snuffling pigs.
The success of the closed carpel can be seen, in part, in the sheer diversity of flowering plants. Angiosperms dominate the vegetation of most continents and islands. There are at least a quarter of a million species of flowering plants, and new ones are found, described, and named every month. In contrast, there are fewer than 800 species of living gymnosperms wearing their seeds in exposed cones and cups. These days, a new species of gymnosperm is rarely found and described more than once every couple of decades. As you will see, there may be benefits to a closed carpel that are not enjoyed by plants that expose their ovules.
Of course, there are important exceptions to the observation that flowering plants always conquer and rule. For example, trees with naked seeds are more likely to fill forests in the northern interiors of the northern continents. There, soils never quite thaw out and evaporation is minimal because winter temperatures may fall as low as -50 degrees centigrade. In these snow forests, cone-bearing spruces (Picea), larches (Larix), and firs (Abies) are likely to form a canopy over the smaller flowering alders (Alnus) and birches (Betula). Most of the densest and broadest gymnosperm forests on this planet are in Canada, Scandinavia, Russia, and Siberia. In most other parts of the world, gymnosperms must compete with flowering plants for their fair share of deserts, savannas, and rain forests.
Flowering plants make up such a huge group that scientists who classify plants have split them into two classes sharing a common evolutionary origin. Angiosperms are classified according to a broad but dependable suite of characteristics shared by the vast majority of species in each class. These include such anatomical features as the construction of the embryo in the seed and the way veins run through stems and then spread out inside leaves. Flowers also play a most important role in this suite of characteristics, as the number of organs in each ring is usually so consistent that botanists can assign each species to one of the two classes.
In some flowers, either there are no more than three organs in each ring (three sepals, three petals, three stamens, three carpels) or the organs in each ring come in multiples of three (six, nine, or twelve carpels). A flower containing organs arranged in threes is most likely to belong to a plant in the class Monocotyledonae. There are more than 65,000 species of monocotyledons, including all grasses, sedges, orchids, pineapples, and true lilies, to name but a few. The word monocotyledon refers to the fact that if you dissect a mature seed, you will find only one large “seed leaf” sheathing the embryo. Popcorn provides a good example. The hard brown spot in the center of a fluffy bit of popped corn is all that remains of the seedling leaf after heat made it explode out of its husk.
The second class of flowering plants, the Dicotyledonae, comprises more than 170,000 species, including almost all flowering trees and thousands of wildflowers. The word dicotyledon refers to an embryo with two seed leaves. These first leaves are familiar to most people as the plump “mittens” on a mung bean sprout or the green “bow tie” tipping an alfalfa seedling. Dicotyledons have the most variable number of organs in a floral circle, alternating between series of fours and fives.
The five brothers in the rose blossom are evidence that rosebushes pledge their loyalty to the Dicotyledonae. Despite mutation and hybridization, we can expect five sepals and five petals in each wild rose. The stamens and carpels in the flower may be too daunting to count, but it is safe to predict that they will occur in increments of five, ten, fifteen, twenty, and so on.
Fascinating as these counting games may be, they are only one of the tricks botanists use to help identify plants. Flowers have many more design secrets that contribute to their distinctiveness and their reproductive success. Prepare yourself for these details and gather another fresh rose.